The present invention relates to a display unit which can superpose a plurality of objects to be viewed which are located at positions having different distances (depths) as viewed from the viewer, with one another and which can display the thus superposed image, to a method of displaying an image which gives a depth feel (three-dimensional effect) and to equipments incorporating thereof.
There have been used direct-view display units for displaying images data, incorporating a display element such as a CRT (cathode ray tube), a plasma display panel, a liquid crystal display element or an organic electroluminescence display element, and a projection display unit for enlarging an optical image formed on a small-sized display element and then displaying the enlarged image on a screen.
Any of these display units displays a two-dimensional image on the basis of two-dimensional image data. It is noted that a display element for displaying a two-dimensional image and a display unit incorporating the same will be denoted as “two-dimensional display element” and “two-dimensional display unit”, respectively.
Of the above-mentioned display units, display units each incorporating a liquid crystal display element which is thin and light-weight, are widely used as in large-sized screen television sets, monitors for personal computers, mobile telephones, game machines including pin ball game machines and pin-ball type slot machines and the like.
By the way, there have been heretofore presented a display unit in which a plurality of two-dimensional display elements or screens of a plurality of two displays are arranged at positions having different depthwise distances as viewed from a viewer, and images thereon are optically superposed with one another and are then displayed in order to allow the viewer to sense depthwise feeling or three-dimensional effects. Such a display unit has a high expressive power in comparison with a display unit which can only display two-dimensional images, and can exhibit a more realistic image.
A typical one of these display units has such a configuration that a plurality of two dimensional display elements and a half-mirror are provided, and a screen of one of these display elements which is viewed, passing through the half-mirror, and a screen of another of the display elements which is viewed, being reflected by the half-mirror, are located at positions having different depthwise distances. Referring to FIG. 43 which is a schematic sectional view illustrating the above-mentioned conventional display unit which comprises two display elements and a half mirror, liquid crystal display elements are used as the two-dimensional display elements, and an image beam (which will be hereinbelow referred to as “far distance image beam”) from a display element located at a position having a far depthwise distance (which will be hereinbelow referred to as “a far distance display element”), as viewed from the viewer, is viewed, passing through the half-mirror while an image beam (which will be hereinbelow referred to as “near distance image beam”) from a display element located at a position having a near depthwise distance (which will be referred to as “near distance image display element”), as viewed from the viewer, is viewed, being reflected by the half-mirror. In this configuration, images which are displayed on the screens having different depthwise distances as viewed from the viewer, are optically synthesized with each other by the half-mirror, and are therefore viewed in a superposed condition.
In the above-mentioned configuration, there are required two two-dimensional elements in such a case that two screens are located at different depthwise distances. That is, in this configuration, a plurality of two-dimensional display elements are required by a number equal to that of screens located at different depthwise distances, and as a result, there is presented such disadvantages that a number of components is increased, and the display unit becomes large-sized. In particular, in such a case that thin display elements such as liquid crystal display elements or organic electroluminescence display elements are used as two-dimensional display elements, their features such that they are thin cannot be fully and practically used.
Further, in the conventional technologies in which the far-distance image beam and the near-distance image beam are synthesized through the half-mirror, the half-mirrors has in general a transmission factor T % and a reflection factor R % which are in total 100% at a maximum. Thus, R % and T % of the far distance image beam and the near distance image beam emitted from the respective display elements cannot be seen by the viewer, that is, they become a beam loss. Thus, there has been raised such a problem that the image beams which can be seen by the viewer are reduced to values not greater than their halves.
JP-A-2003-57595 discloses a display unit which is composed of a plurality of reflection type holographic diffusion plates located at different depthwise positions as viewed from a viewer, and a plurality of projectors for projecting two dimensional images respectively onto the reflection type diffusion plates. The reflection type holographic diffusion plates reflect and scatter light rays in set predetermined directions, that is, light beams from the corresponding projectors, but transmit therethrough light beams in the other directions, such as light beams reflected and scattered from the reflection type holographic diffusion plates located therebehind. Thus, images projected onto the plurality of reflection type holographic diffusion plates located at positions having different depthwise distances can be seen in a superposed condition.
In this case, unless the reflection type holographic diffusion plate has a transmission factor of 100%, the image beam projected onto a reflection type holographic diffusion plate which is located at a position having a depthwise far distance causes a loss before it reaches the viewer.
Further, since it is required to arrange the plurality of reflection type holographic diffusion plates being spaced from one another corresponding to depthwise distances by which the viewer views the images, the device becomes thicker in the depthwise direction. Further, the projectors are required by a number equal to that of the plurality of reflection type holographic diffusion plates, and as a result the number of components is increased, thereby the size of the device becomes larger.
It is noted that JP-A-2003-57595 and JP-A-2000-214413 disclose display methods which allow the viewer to perceive three-dimensional stereoscopic images. In these methods, two-dimensional stereoscopic images (pictures) formed on screens of a plurality of display elements having different depthwise distances as viewed from the viewer, are displayed being superposed with one another when the viewer views these images at a position on a line connecting between the left and right eyes of the viewer. Further, the brightness is adjusted in accordance with depthwise positions of objects to be displayed, that is, distances from the viewer to objects to be displayed while brightness of the two-dimensional images (pictures) displayed on the screens having different depthwise distances as viewed by the viewer is maintained to be constant thereby it is possible to allow the viewer to perceive a three-dimensional stereoscopic image.
The above-mentioned methods can restrain contradictions among physiological factors of stereoscopic vision, and accordingly, these methods can be expected as new three-dimensional display methods which can also reduce the amount of information. However, the position of the viewer where a three-dimensional stereoscopic image can be satisfactorily viewed would be limited. That is, should the view point of the viewer be changed largely, a three-dimensional stereoscopic view could not be viewed.